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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
chemistry
Reduction of Escherichia coli ribonucleotide reductase subunit R2 with eight water-soluble ferrocene derivatives
Inorganica Chimica Acta, Volume 337, Year 2002
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Description
Water soluble ferrocenes [Fe(Cp)(CpL)], where Cp- is the η5-cyclopentadienide ligand and the side chain L is (a) the carboxylic acid group -(CH2)xCO2H with x=0-4 (I-V); (b) the complex x=2 with the β-methylene mono-methyl substituted (VI); (c) the amine hydrochloride derivative with L=CH(Me) NH3+ (VII); and (d) the complex with two Cp rings bridged by the amine hydrochloride -CH(NH3+)CH2CH2- (VIII); have been prepared, and are used as one-equivalent reductants for the active-R2 subunit of Escherichia coli ribonucleotide reductase. Formal reduction potentials E1°′ (25°C) of the carboxylates of acids I-VI in 20 mM NaOH, and of the amine hydrochlorides VII and VIII in water were determined by cyclic voltammetry, and are in the range 0.308-0.550 V versus nhe, I=0.100 M (NaCl). Second-order rate constants k12 (25°C) for the reduction of active-R2 were determined by UV-Vis spectrophotometry, and are in the range 0.15-0.50 M-1 s-1 at I=0.100 M. A free-energy plot of logk12 versus E°′ values gives no clearcut unidirectional trend. Since from present information the electron self-exchange rate constant for the [Fe(Cp)2]+/[Fe(Cp)2] couple is favourable (>7×106 M-1 s-1 in methanol at 25°C), it would appear that electron-transfer from the ferrocenes via Trp-48, Asp-237, His-118 to the FeIII2 site on R2 is much slower than expected, and smaller than with the organic radical reductants previously studied. Electron-transfer from some other position on the protein surface to the Tyr· is considered as an alternative. © 2002 Elsevier Science B.V. All rights reserved.
Authors & Co-Authors
Liu, Aimin
United Kingdom, Newcastle
Newcastle University
Leese, David N.
United Kingdom, Newcastle
Newcastle University
Swarts, Jannie C.
South Africa, Bloemfontein
University of the Free State
Sykes, A. Geoffrey
United Kingdom, Newcastle
Newcastle University
Statistics
Citations: 12
Authors: 4
Affiliations: 2
Identifiers
Doi:
10.1016/S0020-1693(02)01102-7
ISSN:
00201693
Research Areas
Environmental